Very large catfish are a more probable monster. The exist and are fairly common. I had a friend who fished the Arkansas River commercially. He later became a navy SEAL. He refused to swim in the river after encountering the giant catfish he’d seen.

not quite the most objective kind of video, let’s be frank: kids drow in lakes and other swimming area all the time, sometimes right under the nose of an experienced lifeguard, but suggesting or speculating it’s a giant octopuss is ludicrous, one could with the same lack of evidence speculate it’s an underwater station of extraterrestial aliens.